1. Field of the Invention
The present invention relates to a method of manufacturing a negative electrode for a solid-state battery, a method of manufacturing a solid-state battery, and a negative electrode slurry.
2. Description of Related Art
As a battery having high safety, a solid-state battery is known. The solid-state battery includes: electrodes that include an active material; and a solid electrolyte layer that is a separator layer interposed between the electrodes. The electrodes or the solid electrolyte layer can be easily manufactured using a slurry in which an active material or a solid electrolyte is dispersed in a solvent. For example, as described in Japanese Patent Application Publication No. 2013-118143 (JP 2013-118143 A), a desired electrode layer can be obtained through the following steps of: mixing an electrode active material, a sulfide solid electrolyte, a binder, and a solvent to prepare a slurry; applying the slurry; and drying the slurry.
In the related art, for example, polyvinylidene fluoride is used as a binder. When polyvinylidene fluoride is used as a binder, for example, N-methylpyrrolidone can be preferably used as a solvent from the viewpoint of the solubility of polyvinylidene fluoride. However, as a result of thorough research, the present inventors found that N-methylpyrrolidone reacts with a sulfide solid electrolyte to decrease the lithium ion conductivity of the electrolyte.
On the other hand, when an ester-based solvent such as butyl butyrate or an ether-based solvent such as dibutyl ether is used as a solvent, there is a problem in the solubility of polyvinylidene fluoride in the solvent. From this point of view, in the related art, a copolymer of vinylidene fluoride with another monomer is used as a binder to adjust the solubility of the binder in a solvent. As the binder, a three-component copolymer of vinylidene fluoride (VDF), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE) is particularly preferable. However, as a result of thorough research, the present inventors found that, when such a three-component binder is used, the battery capacity decreases during initial charging.
In addition, when polyvinylidene fluoride or a three-component copolymer of VDF, HFP, and TFE is used as a binder as in the related art, the adhesive force between a current collector and an electrode layer is not sufficient, and the peeling or cracking of an electrode may occur during the manufacture of a solid-state battery.
As described above, in the related art, when a negative electrode for a solid-state battery is manufactured, the following effects of preventing deterioration of a sulfide solid electrolyte, securing a sufficient adhesive force between a current collector and an electrode layer, and suppressing capacity deterioration caused by a negative electrode, cannot be simultaneously obtained.